|Jerome J. Lazar, RA, CCS, CSI, SCIP
Post Number: 166
|Posted on Wednesday, October 05, 2005 - 12:27 pm: |
When do you use SBS versus APP bitumen modifiers? Preferable comments for hot and humid climates.
Loaded question - is one system better than the other?
Horror stories welcome!
|Doug Frank FCSI CCS
Post Number: 125
|Posted on Wednesday, October 05, 2005 - 12:37 pm: |
Horror Stories huh? How about this one: Several years ago I was responsible for a reroofing project where we planned to install a new 2-ply APP modified bitumen roof membrane over an existing smooth-surface BUR. It was the roofing contractor’s very first experience with a “torch-applied” modified bitumen system. The first day on the roof I reminded the roofer about the need for a Fire Extinguisher on the job. The second day, and the third day I reminded him again. On the fourth day there was a fire extinguisher on the roof,,,, but completely discharged! Finally got going and a few days later, when making a late afternoon site visit I noticed wisps of smoke coming from under some metal counterflashing (the roofers had progressed about 30 feet away by then). Luckily I chose that time of the day for a site visit. Luckily they had a working fire extinguisher. We almost burnt the Houston Astrodome down!!!!!
I haven’t spec’d a torch-applied APP system since; I use SBS systems applied in Hot Type IV asphalt only.
|Richard L Matteo, AIA, CSI, CCS
Post Number: 121
|Posted on Wednesday, October 05, 2005 - 12:40 pm: |
I'm told by most of my roofing reps that sell the stuff that SBS is a better product.
The thing to be careful of is a torch-applied system.
It has become a major issue here in California, and most roofers have tended to shy away from it, due to insurance issues and the potential for fire.
We have pretty much decided to use cold-applied SBS systems unless requested otherwise by the Client/Owner.
A former employer once told me "nothing made him happier than when an owner told him what type of roof system to use".
Post Number: 140
|Posted on Wednesday, October 05, 2005 - 12:55 pm: |
SBS is a thermoplastic rubber. It increases flexibility over a wider temperature range than APP, and can remain flexible at temperatures below minus 10 deg F. Adding SBS polymer to asphalt flux can increase the softening point from approximately 90 to 260 deg F.
APP is a thermoplastic material that can increase the softening point of an asphalt from 90 to 300 deg F, and can provide the product with more tensile strength.
We prefer SBS because it is not as brittle in low temperatures as APP. I do like torch-applied, but if we are applying it to a wood structure I’ll specify mopped not torched.
|John Bunzick, CCS, CCCA
Post Number: 417
|Posted on Wednesday, October 05, 2005 - 02:07 pm: |
As an interesting historical note: atactic polypropylene was at one time a byproduct of other chemical manufacturing, and had little commercial value. Then the roofing market (and possibly others) found it useful as a modifier. After the market for APP demand soared, chemical companies had to start to make more of it since the demand exceeded its production as a byproduct.
Dave already made the points I was going to about flexibility. Not too keen on torches, either.
Since it was brought up, does anybody want to chime in about the use of cold-applied versus hot-applied sytems? Are the cold-applied equal in durability (cure-time issues not withstanding)? How about self-stick?
|Anne Whitacre, CCS CSI
Post Number: 259
|Posted on Wednesday, October 05, 2005 - 02:14 pm: |
we use the cold applied regularly out here because they seem to have less odor, and we especially use them in health care work. (assuming we want a modified bitumen roof in the first place). I have seen no difference in longevity, but that assumes we have a good roofing contractor. And of course, the northwest is a fairly benign climate -- very little freeze/thaw, and very few really warm days.
|George A. Everding, AIA, CSI, CCS, CCCA
Post Number: 76
|Posted on Wednesday, October 05, 2005 - 03:15 pm: |
I've always done SBS hot mopped because I had concerns about long term durability with cold applied, but it sounds like that is no longer an issue. I think the trend to cold applied is a good thing (lower voc's and no kettles) and probably will end up in that camp before too long.
By the way, roofing reps here (St. Louis) tell me APP is a very very small part of our low slope market. SBS is overwhelmingly the mbr choice here.
|William C. Pegues, FCSI, CCS
Post Number: 499
|Posted on Wednesday, October 05, 2005 - 04:04 pm: |
We had a number of minor but very irritating problems (due mostly to intallation error than anything else) with cold applied systems, so we tend to stay away from them in our practice here. Our office standard for roofing is hot fluid applied reinforced membrane. We have never had a problem with a roof, and I have a number of roofs that were installed 25+ years ago. We use the same system for horizontal plaza and direct applied vertical waterproofing.
The major manufacturer's of the system have all moved away from flame kettles now, they aer all typically electric. Actually, in the IBC (and some of the UBC later versions) there is a requirement that limits the type of kettles that can be put on the structure of a building during construction. Due to some very poor wording, though the intent was to ban open flame kettles, they used some very broad wording that might lead one to believe it bans all hot roofing kettles.
The nice thing about these systems are the ability to even convert an existing roof over to a garden (vegetated) roof and work with the manufacturer to have a warranted system with the conversion.
Post Number: 136
|Posted on Friday, October 07, 2005 - 12:09 pm: |
We do a majority of our institutional roofs in 2-ply SBS MBs or in hybrid BUR felts with MB cap sheets. We've been moving away from hot applieds, and recently note 3 projects where roofing installers asked to use cold rather than hot systems for their convenience.
Our reps cite avoidance of moisture-related blistering as another reason to go to cold-applied systems for SBS MBs. Although we haven't had a problem, apparently there's enough experience with that to warrant their preference.